M33

I gave this quite a long exposure with the H alpha filter (c7.5 hours) since I wanted to capture the various hydrogen clouds. The image represents about 15 hours of integration.  CCDstack used for calibration, stacking and error rejection. Pixinsight for DBE, BN and Colour Calibration, PS for everything else.

The major challenge with this image is that it contained various scattered light "rainbows" that where generated by out of view bright stars, one of these "rainbows" passed straight through the galaxy. To eliminate the scattered light issue I followed the PS tutorial by Adam Block in his "cosmic canvas" series - this is an amazingly effective technique to eliminate/reduce the problem.

LIGHTS:  L:15, R:9, G:10, B: 12 x 600s; H: 15 x 1800s. DARKS:30; BIAS:100; FLATS:40 all at -20C.